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Bioelectric Extension Cord (Jan 2005)
Docking of cyt c2 to reaction center

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Energy for most of the earth's biosphere is gained when sun light absorbed drives electrons across a membrane through a protein called the photosynthetic reaction center (RC), leaving behind positive electron holes. The electrons join protons to become hydrogen atoms and move, bound pairwise to a quinone molecule, to another protein, the so-called bc1 complex. Here electrons and protons move together back over the membrane and become separated again, thereby establishing an electro-osmotic potential that fuels many cellular processes. However, the electrons need to return to the RC to fill the electron holes left behind. Nature employs for this purpose a kind of bioelectric extension cord in the form of a third protein, cytochrome c2, that shuttles the electrons back from the bc1 complex to the RC. A recent paper reports molecular dynamics simulations using NAMD that investigated how cytochrome c2 plugs into the RC. Landing on a broad face of the RC, interactions steer the protein such that its electron carrying heme group comes close to RC's chlorophylls with electrons missing, a chain of water molecules providing an electrical conduit. The study is yet another example of how simulations provide today complete views of the fundamental processes underlying life.